Science 1194 SAS Curriculum Pathways Chemical Equations: Journal

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1 Chemical Equations: Journal NAME: ray CLASS: chem90 DATE: 10/27/2013 FOCUS QUESTION: How and why are chemical equations balanced? TAB 1: Equations Read the questions below. Then complete this Journal by interacting with the online Simulation. Remember: the Journal does NOT check your answers. Review your text entries and make sure you've transferred data to the correct table rows. Chemical equations represent what happens during the course of chemical reactions. Reactants and products, their quantities, and their physical states can be represented, as in the following equation: Zn (s) + 2 HCl (aq) ZnCl 2 (aq) + H 2 (g). In words, solid zinc reacts with aqueous hydrochloric acid (hydrogen chloride) to yield aqueous zinc chloride and hydrogen gas. The "2" in front of HCl is called a coefficient. Coefficients indicate the simplest, whole-number ratios between the substances in the reaction. Their purpose is to ensure that the equation is balanced and that matter is conserved. In a balanced equation, the number of atoms of an element on the reactant side of the equation equals the number of atoms of that same element on the product side. In this section, you will learn how to count the number of atoms within a substance and to recognize balanced and unbalanced chemical equations. In the Simulation (to the right) select a reaction from the pull-down menu. Drag the molecules to the twopan balance to count the numbers of reactant and product atoms and to determine if the equation is balanced. 1.1 Data Collection For each chemical reaction: Pay attention to the Data panel as you drag each molecule to the balance. Observe how the atom counts change. Use the Transfer Data button ( ) to transfer the atom count from the Data panel to the table. Then, use the pull-down menus to indicate if each substance is balanced. Reaction 1: CO + 2 H 2 CH 3 OH elements: C O H # of reactant atoms: # of product atoms: balanced? yes yes yes Reaction 2: Fe 2 O Mg MgO + 2 Fe elements: Fe O Mg # of reactant atoms: # of product atoms: balanced? yes no no Reaction 3: 2 NH 3 + O 2 2 NO + 3 H 2 O elements: N H O # of reactant atoms: # of product atoms: balanced? yes yes no Copyright 2013, SAS Institute Inc., Cary, NC, USA, All Rights Reserved Page 1 of 6

2 Reaction 4: (NH 4 ) 2 PtCl 6 2 NH 4 Cl + Pt + 2 Cl 2 elements: N H Pt Cl # of reactant atoms: # of product atoms: balanced? yes yes yes yes Reaction 5: 2 C 2 H O 2 4 CO H 2 O # of reactant atoms: # of product atoms: balanced? yes yes yes 1.2 Name and state the law requiring chemical equations to be balanced (discussed in the Welcome video). It is the law of conservation of mass. It states that the mass is neither created nor destroyed. Thus, the mass in the reactacnt should be the same in the product. 1.3 For Reaction 2, putting a coefficient of 3 in front of MgO produces a balanced equation. Explain why the equation cannot be balanced by changing MgO to Mg 3 O 3. Putting in front 3 MgO is technically not allowed. Besides the law of definite composition states that chemical compounds are composed of fixed ratio of elements by mass. Thus there's only MgO and not Mg3O3 1.4 Can Reaction 3 be balanced by putting a coefficient of 5/2 in front of O 2? Why or why not? It can be balanced but it is not customary to leave coeficients as fractions. We need to multiply coefficients in both sides by two as per the law of multiple proportion which states that masses of one element which combine with a fixed mass of second element are in a ratio of whole numbers. 1.5 In Reaction 4, 2 NH 4 Cl molecules are formed. In total, how many atoms of each element do these two molecules contain? Explain your reasoning. N = 2 H = 8 Cl = 2.In doing so, we only need to multiply each coefficient with the subscript to obtain the number of atoms in each element. So for N its 2x1 = 2. for H its 2x4=8 and for Cl its 2x1= In Reaction 5, the atom count for oxygen is 14. Explain how the product side of the equation represents 14 oxygen atoms. In 4O2 the number of Oxygen atoms is 4x2 = 8 In 6H2O the number of oxygen atoms is 6x1 = 6 So 6+8 there are now 14 oxygen atoms in total TAB 2: Balancing In this section, you will develop your equation-balancing skills. The process of balancing a chemical equation could involve trial and error, but having a procedure to follow makes the task simpler. To view a step-by-step process, click the "how-to" button. In the Simulation (to the right) select a reaction from the pull-down menu. Balance the equation by dragging substances to the reactant and product areas. The Simulation displays a Congratulations message when the equation is correct. Pay close attention to the Data panel as you work. Copyright 2013, SAS Institute Inc., Cary, NC, USA, All Rights Reserved Page 2 of 6

6 Answer to Focus Question: Equations should be balanced in accordance with the law of conservation of mass which states that the mass is neither created nor destroyed which means we have to balance equation such that the mass in the reactant is the same as the product. In balancing equation it is the coefficients that we can change. To balance equation, we need to find the right coefficients in the reactants and products that will yield the same number of atoms of each elements in each side. Answer to balancing equation: 3 Cu(NO3)2 + 2Na3PO4 -> 6NaNO3 + Cu3(PO4)2 Copyright 2013, SAS Institute Inc., Cary, NC, USA, All Rights Reserved Page 6 of 6

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